This invention relates to improvements in wear compensating energy-absorbing span lock systems, such as disclosed in U.S. Pat. Nos. 5,327,605 and 6,588,041 assigned to Steward Machine Co., Inc.
In the '605 patent, FIG. 1 illustrates in plan view a span lock mechanism connecting aligned ends of a double leaf bascule bridge. FIGS. 7a, 7b and 7c illustrate schematically the motion of a locking bar that connects the ends. Resilient elements are illustrated as Bellville-washer type springs that engage shoes which bear on the end portion of the locking bars to effect the desired resilient connection of the span leafs across their ends.
In the '041 patent, an adjustable pre-load mechanism is provided to maintain a desirable level of continuous contact load pressure between the shoes and locking bar, and to afford manual compensation for wear that may occur over prolonged periods of time in service.
While the mechanisms disclosed in these Patents function satisfactorily for their intended purposes when properly maintained, there is a need to provide an improved mechanism to minimize wear between the shoes and locking bar in an automatic manner when bridges are installed and maintained under less than desirable conditions and environments.
One way to do this contemplates the use of hydraulic cylinders to press the shoes into firm contact with the lockbar with hydraulic pressure while the spans are locked, such as disclosed in FIG. 11 and Col. 5, Lns. 38-43 of the '605 patent. A problem with this concept is that hydraulic pressure would need to be maintained continuously while the bridge is locked for land vehicular traffic. This requires power and costs associated with continuous power, or could require accumulators to maintain contact pressure. The present invention overcomes the disadvantage of the aforedescribed concept by providing a mechanism that eliminates the need for continuous power while the bridge is locked and requiring power only when needed to open and close the bridge. Since bascule bridges are normally locked, and only occasionally opened for passing marine vehicular traffic, substantial savings in overall power consumption can be achieved over the continuous pressure concept referenced.